Lately, I mentioned a local electronics shop, I guess they would also ship outside the Netherlands. As noted in the previous entry, they have some uncommon crystals in the assortment.
The specific one I would like to focus on today will enable 136kHz action, either by mixing with another crystal, or as superhet design with a couple of options.
Here we go, have a look at 4233.6kHz.... mix it with 4096kHz will get us to 8329.6kHz aaahhh... hmmm.... and:
According to the band-plan, this is spot on for the lower edge of the QRSS section! Since at about 4MHz crystals can easily be pulled a couple of kHz, the whole band is easily covered.
You already guessed, we will have some options for superhet design too. I would recommend the filter being made from 4096kHz crystals, reason being the better availability. Additionally, the 4096kHz intermediate frequency allows for a 2048kHz subharmonic BFO.